Monday, July 13, 2015

Importance of Color Reproduction in Scientific Images

Human eyes receive light via two photoreceptors: cones and rods. When looking at objects under different lighting conditions, humans tend to see the same objects as having the same color. For example, an apple will appear red whether it is lit by daylight or a candle, and a white sheet of paper will be perceived as being white no matter the light source. This is known as chromatic adaptation or color constancy.

When it comes to viewing microscopic specimens with a monitor or capturing microscopy images with a microscope camera the colors perceived through the eyepieces will differ from those viewed on the screen or captured in the camera. Color reproduction is a key and important part of capturing scientific images. For example, when viewing a histology slide that has been stained with hematoxylin and eosin, if the colors are not represented properly the slide could be diagnosed improperly. Images need to be compared to previous samples and poor color reproduction could lead to problems.

In image processing, chromatic adaptation is referred to as "white balance" or "color balance". Electronic image sensors and processors don't match human cones and rods and therefore color correction is an important component of capturing microscopy images.

Microscope cameras with CCD or CMOS sensors are sensitive to infrared (IR) light, which can have the effect of reducing image contrast. Some cameras incorporate IR filters that can compensate for this sensitivity. Microscope filters are also used to compensate in this area as well.

Color reproduction will vary between microscopes, room set-up, and lighting conditions. In addition, colors vary depending on samples, stains and fluorophores that are used. When possible, always use the same microscope system and ensure it is correctly aligned for Koehler Illumination.

Koehler Illumination is a method that provides optimum contrast resolution by focusing and centering the light path and spreading it evenly over the field of view. This process is used to achieve bright and even illumination across the sample, while ensuring that the illumination source is invisible to the resulting image. This helps create the best possible image quality and Koehler illumination is the method of choice for the majority of modern biological microscopes.